NameSemester: 1st

Department of PsychologyUniversity of Kashmir.

INTRODUCTION:

• Pregnancy is broken down into weeks, and is divided into three parts called trimesters.Full term pregnancy is considered 40 weeks and an infant delivered before the 37th week is considered premature.

The first, second, and third months are the first trimester of pregnancy.

CONCEPTION

• The first step of prenatal development begins to unfold with conception.

• Conception or fertilization is the union of male and female gamete (sperm & ovum).

• Gamete(or sex cells) is a mature haploid male or female germ cell which is able to unite with another of the opposite sex to form a zygote.

• The cell resulting from the uniting of the male and female gamete is called ZYGOTE.

THE GERMINAL PERIOD (2 Week)• Once fertilization has taken place, the zygote begins dividing and

moving down to the uterus , the muscular organ that will contain & protect the developing infant. This process takes about a week, followed by another week during which the mass of cells, now forming a hollow ball (blastocyst) , firmly implants itself to the wall of the uterus. This two-week period is called the germinal period of pregnancy.

• The placenta also begins to form during this period. The placenta is a specialized organ that provides nourishment and filters away waste products from the developing baby. The umbilical cord also begins to develop at this time, connecting the organism to the placenta.

• Structures that feed and protect the developing organism begin to form- Yolk sac, placenta, umbilical cord.

• Umbilical cord, is the long cord connecting the prenatal organism to the placenta.

Normal Progression Of Development For The First 10 Days Of Gestation

THE PERIOD OF THE ZYGOTE• Once every 28

days, an ovum matures, is released from one of the woman’s ovaries and is drawn to the fallopian tube.

• After fertilization, zygote will undergo multiple rounds of cleavage, or cell division, in order to produced a ball of cells, called a blastula.

Cleavage, Blastula & Gastrula• The zygote will undergo multiple

rounds of cleavage, or cell division, in order to produced a ball of cells, called a blastula, with a fluid-filled cavity in its center, called a blastocoel.

• The blastula eventually organizes itself into two layers: the inner cell mass (which will become the embryo) and the outer layer or trophoblast (which will become the placenta); the structure is now called a blastocyst.

• During gastrulation, the blastula folds in on itself to form three germ layers, the ectoderm, the mesoderm, and the endoderm, that will give rise to the internal structures of the organism.

END OF GERMINAL PERIOD

TERMS• Blastula: a 6-32-celled hollow structure that is formed after a zygote

undergoes cell division.• Trophoblast: the membrane of cells that forms the wall of a blastocyst during

early pregnancy, providing nutrients to the embryo and later developing into part of the placenta.

• Blastomere: any cell that results from division of a fertilized egg. • Gastrulation: The cells in the blastula rearrange themselves spatially to form

three layers of cells in a process known as gastrulation. During gastrulation, the blastula folds upon itself to form the three layers of cells. Each of these layers is called a germ layer, which differentiate into different organ systems ( Endoderm, Mesoderm, Ectoderm).

• Cleavage: The repeated division of a fertilized ovum, producing a cluster of cells with the same size as the original zygote.. The cells in the blastula rearrange themselves spatially to form three layers of cells in a process known as gastrulation. During gastrulation, the blastula folds upon itself to form the three layers of cells. Each of these layers is called a germ layer, which differentiate into different organ systems .

4th Week Of Pregnancy

THE EMBRYONIC PERIOD(2-8 Weeks)

• Once firmly attached to the uterus, the developing organism is called an embryo. The embryonic period will last from two weeks after conception to eight weeks, during this time the cells will continue to specialize and become the various organs and structures of human infant. By the end of eight weeks after conception, the embryo is about 1 inch long and has primitive eyes, nose, lips, teeth, little arms and legs, digestive tract and a beating heart.

• During these brief 6 weeks, the most rapid prenatal changes take place, although no organ is fully developed or completely functional at this time, nearly all are there.

• The sense of touch begins to develop, and the embryo can move.

6th Week Of Pregnancy

7th Week Of Pregnancy

LAST HALF OF THE FIRST MONTH

• In the first week of the embryonic period, the blastula folds in on itself to form three germ layers, the ectoderm, the mesoderm, and the endoderm, that will give rise to the internal structures of the organism.

• The Ectoderm, which will become the nervous system and skin;• The Mesoderm, which will develop the muscles, skeleton,

circulatory system, and other internal organs;• The Endoderm, which will become the digestive system, lungs,

urinary tract, and glands.

• These 3 layers give rise to all parts of the body.

Differentiation Of Germ Layers

THE SECOND MONTH

• In the second month, growth continues rapidly. The eyes, ears, nose, jaw and neck form. Tiny buds become arms, legs, fingers and toes.

• Internal organs are more distinct: the intestines grow, the heart develops separate chambers.

• Now 1 inch long and 1/7 of an ounce on weight, the embryo can already sense its world.

Two Months

CRITICAL PERIOD

• As soon as the embryo begins to receive nourishment from the mother through the placenta, it becomes vulnerable to hazards such as diseases of the mother, drugs and other toxins that can pass from the mother through the placenta to the developing infant.

• This time of pregnancy is called the critical period, times during which some environmental influence can have an impact-often devastating-on the development of the infant.

CRITICAL PERIODS IN PRENATAL PERIOD

Body System - Especially Sensitive Development

• Central nervous system/Brain - 4th to 8th weeks• Heart - 5th to 9th weeks• Upper limbs- 6th to 10th weeks• Eyes- 6th to 10 weeks• Lower limbs - 6th to 10th weeks• External genitalia- 9th to 11th weeks

PRENATAL ENVIRONMENTAL INFLUENCES

• Teratogens are environmental agents that cause damage during the prenatal period. Their effects usually conform to the critical period. The organism is especially vulnerable during the embryonic period when body structures are rapidly emerging.

• The effects of teratogens is not limited to immediate physical damage. Serious psychological consequences may appear later in development.

• Drugs, cigarette smoking, alcohol, hormones, radiation, environmental pollution, and certain infectious diseases are teratogens that can endanger the prenatal organism.

EFFECTS OF TERATOGENS ON DEVELOPMENT

THE FETAL PERIOD• The fetal period is the time from about eight weeks after conception

until the birth of the child (now called a fetus) and is a period of tremendous growth.

• However, in the first trimester we consider only 8-12th week.• During this time, nervous system, organs and muscles become

organized and connected, and new behavioral capacities appear ( the brain signals & in response the fetus kicks, bends its arms, opens its mouth, curls its toes etc).

• The heartbeat is now stronger. The head now appears very large compared to the rest of the body because the brain is growing rapidly.

• By the end of the third month, the developing baby is about four inches long, weighs a little over an ounce, and signs of the baby's sex are beginning to appear. Finger and toenails are developing. The mouth opens and closes and the baby will begin to move its hands, legs, and head. The mother will not yet be able to feel this movement.

BIBLIOGRAPHY

• Berk E. Laura, Child Development, Fourth edition• Meyer Glenn, Psychology• Bee Helen, The Developing Child, Eighth Edition• http://americanpregnancy.org/

duringpregnancy/fetaldevelopment1.htm• http://www.webmd.com/baby/1to3-months• http://www.biology-online.org/dictionary/

Cleavage